Metal covered composite yarns have been known for many years and are essentially formed by a fibrous, non-metallic core covered with a thin metal foil ribbon or band having high reflecting properties, e.g. made of gold, silver or copper.
The composite yarn so obtained has a pleasant and highly glossy appearance and may be woven, knitted or variously disposed to make fabrics, clothing products, necklaces, earrings, rings and other fashion accessories in general.
U.S. Pat. No. 3,126,698 discloses a composite material, lame yarn, for use in production of fabrics and similar articles, which yarn is formed by a natural or synthetic, non-metallic core covered with a spirally wound metallized band.
The metallized band is formed by a transparent and flexible, thermoplastic base made of cellophane, acetate, Mylar or the like, on which a metal film made of gold, silver, aluminum, magnesium, titanium or nickel is deposited. Metal deposition may be carried out by various sputtering, electrodeposition or positive-ion bombardment techniques. The metallic layer may be coated with colored solutions or suspensions, having both an aesthetic and protective function. The composite yarn core may be formed by one or more filaments made of glass, nylon or natural or synthetic silk, in variable amounts depending on the desired structural strength.
This known metallized yarn has a higher softness than prior lame yarns, however the core is still rather stiff and has some elastic memory, especially when considering the friction existing between fibers due to the compression exerted by the outer metal cover. Moreover, the plating precious metal is provided in very small amounts, hence the final fineness of the yarn does not meet gold-making and jewelry market requirements and does not comply with regulations for gold-making practice.
U.S. Pat. No. 3,783,081 discloses an ornamental element for the fabrication of jewelry items, which element is formed by a yarn made of a first central rectilinear filament on which a second filament is spiraled, wherein the first and second filaments are at least partly made of a precious metal, such as gold or silver. The thus obtained yarn is then transversely compressed between opposed rollers, to form a flattened ornamental element. The flattened element is finally subjected to a thermal treatment to remove internal stresses caused by mechanical compression forces.
The finished ornamental element may be variously braided, woven, shaped and added to other ornaments to form a sort of “filigree,” which may be used to fill empty spaces of jewels and create ornaments at a relative low cost, as compared with solid precious metal. A drawback of this prior art ornamental element is its relative stiffness, due to the fact that both its central core strand and its outside strand are at least partly made of metal and accordingly has a certain stiffness and a high elastic memory. Moreover, as the outer surface of the yarn is subjected to a compression step, its overall aspect is not sufficiently bright and glossy and has a relatively low ornamental attractiveness.
Other metallized composite yarns, to be used for ornamental purposes or as electric wires, are known from U.S. Pat. No. 4,387,555, FR-A-2643914, U.S. Pat. No. 5,201,169, U.S. Pat. No. 3,361,616, EP-A-399721, U.S. Pat. No. 5,927,060, EP-A-0 911 435 and U.S. Pat. No. 5,632,137.
Also, these prior art composite yarns do not have a sufficiently compliant and light core to provide a highly soft and flexible yarn. Moreover, when these yarns are used for ornamental purposes, their precious metal fineness is relatively lower than that of the jewel or golden product in which it is integrated. Finally, the metal covering foil is often suffering delamination, whereby the aesthetic characteristics of the product may be damaged or impaired.
The present invention relates to a metal covered composite yarn, which is particularly but not exclusively designed for ornamental purposes. The composite yarn of the invention may be generally employed in the field of jewelry, goldsmith art, costume jewelry, textile industry, or for the manufacture of jewels, fashion items and similar objects having a considerable softness and lightness as well as a relative low price.
Thanks to the high electrical conductivity of the metal cover, the composite yarn of the present invention may be also advantageously used as a highly flexible electric conductor applicable in the fields of electric or electronic apparatus, computer, nano-technology and aerospace industry. The invention further relates to a method of manufacturing the above-mentioned composite yarn.